Sputtering apparatus

ABSTRACT

Sputtering apparatus of the glow discharge type operable at relatively low gas pressures and utilizing a combination of magnetic and electric fields and at least one cathode disposed within the magnetic field and constituting a source of atoms which are emitted through a path defined by the cathode for deposition of thin films on a suitable supporting surface.

United States Patent 3,400,066 9/1968 Caswell et a1 204/192 FOREIGNPATENTS 702,672 l/l965 Canada 204/192 939,275 10/1963 Great Britain204/298 OTHER REFERENCES Ll. Maissel, The Deposition of Thin Films byCathode Sputtering," Physics of Thin Films, Vol. 3, pp. 61- 129.Academic Press, 1nc. NY. 1966 Primary Examiner-John H. Mack AssistantExaminer-Neil A. Kaplan Anorney-Eugene E. Geoffrey, Jr.

ABSTRACT: Sputtering apparatus of the glow discharge type operable atrelatively low gas pressures and utilizing a combination of magnetic andelectric fields and at least one cathode disposed within the magneticfield and constituting a source of atoms which are emitted through apath defined by the cathode for deposition of thin films on a suitablesupporting surface.

SPU'I'I'ERING APPARATUS This invention relates to sputtering. apparatusfor production of thin films of metal and dielectric material and morespecifically to a novel and improved sputtering device wherein cathodedisintegration is effected by an electric glow discharge and cooperatingmagnetic field in an improved manner that permits operation at very lowgas pressures and provides films having adherence adherence and improveduniformity in mechanical and electrical properties.

The production of thin films utilizing cathode disintegration is wellknown and is effected by gas ions impinging upon the cathode andphysically ejecting atoms from the cathode surface. This phenomenon isgenerally known as sputtering and is particularly useful for coatingbodies with thin films. [n coating a body, it is generally positioned inthe path of the atoms ejected from the cathode surface so that the atomswill be deposited on the surface of the body. in addition to theutilization of an electric field to produce the glow discharge, magneticfields have been employed in an effort to obtain some improvedoperation. However, known devices whether using an electric field aloneor in combination with a magnetic field have not been found to beentirely satisfactory for a number of reasons. For instance, knownsputtering devices including those using magnetic fields requirerelatively high, gas pressures with the result that the gas atoms withinthe device tend to deflect many of the sputtered atoms away from thebody to be coated causing relatively low deposition efficiency.Furthermore. the relatively high number of gas atoms present in theapparatus causes many of them to become entrapped in the metal filmbeing deposited producing nonuniform films wherein the density variesthroughout the area of the film. Known devices also require that thesurface to be plated either form part of the anode or cathode or bepositioned in the apparatus in such a manner that operation of theapparatus must be terminated upon completion of the coating operation inorder to insert a new workpiece of pieces to be coated, and substantialdifliculty has been experienced in attaining satisfactory adherence ofthe film to the substrate or workpiece.

With this invention which embodies a novel and improved arrangement ofelements including electric and magnetic fields, many difficultiesheretofore encountered with known devices have been overcome and animproved device is provided having a relatively high deposition ordisintegration efficiency, producing a film of substantially uniformdensity throughout its area, and greatly improved adherence of the filmto the work surface whether the work surface is conductive ornonconductive. By the improved coordination of the electric and magneticfields, the magnetic field in accordance with the invention functions todeflect electrons from the paths they would non-nally follow in theabsence of such magnetic field, and furthermore directs the electrons insuch a manner that the lengths of the paths are greatly increased. Thisaction greatly increases the number of ionizing collisions between theelectrons and the gas molecules. As a result, the gas pressure inapparatus in accordance with this invention can be materially reducedwhile at the same time maintaining a relatively high discharge current.Furthermore, since the invention facilitates the use of relatively lowgas pressures the deposition efficiency is greatly improved and agreatly increased quantity of the liberated atoms will be deposited onthe surface to be coated. in addition, the material reduction in thenumber of gas atoms present within the device results in a correspondingreduction in contamination of the film by the inclusion of gas atomstherein. Through an improved arrangement and organization of elementsthe substrate or workpiece being coated assumes an automatic high-biasvoltage which provides a vastly improved film having excellentadherence. This is particularly importantin the case of nonconductivesubstrates.

Another object of the invention is to produce a novel and improvedrelatively high-efficiency sputtering device for coating surfaces withthin films wherein the surfaces to be coated need not form part ofeither the anode or the cathode.

Still another object of the invention resides in the provision of anovel and improved sputtering apparatus utilizing a relatively low gaspressure and at the same time producing a highly stable and intense glowdischarge between the cathode and the anode which greatly facilitatesoperation of the apparatus and produces high quality, high-densityfilms.

A still further object of the invention resides in the provision of ahighly efficient and stable sputtering device that is adaptable for usein normal production operations in that a plurality of individualsurfaces may be successively coated without interrupting the operationof the device.

The above and other objects of the invention will become more apparentfrom the following description and accompanying drawings forming part ofthis application.

in the drawings:

FIG. I is a cross-sectional view of one embodiment of the apparatus inaccordance with the invention and which ernbodies a glow dischargedevice.

FIG. 2 is an enlarged cross-sectional view of the glow discharge deviceillustrated in FIG. I; and

FIG. 3 is a modified form of a glow discharge device in accordance withthe invention.

Referring now to FIG. I, the sputtering apparatus in accordance with theinvention includes a baseplate 10 disposed in a substantially horizontalposition and having a bell jar ll removably sealed to the top surface ofthe plate 10 by suitable sealing means 12. The sputtering apparatus isgenerally denoted by the numeral 13, and as will be described, is sealedto the bottom side of the baseplate l0 and opens into the interior ofthe bell jar I l. A circular work-supporting plate 14 is disposed withinthe bell jar and is pivotally mounted at 15 to the upper surface of theplate Ill. The plate 14 can be rotated by any suitable means as forinstance a motor 16 carrying a drive wheel 17 of resilient materialwhich contacts the periphery of the plate 14. It is evident that otherforms of work or substrate supporting surfaces may also be used.

A conduit 18 extends through the baseplate and is connected on its outerend to a two-way valve l9. A second conduit 20 connects the valve to avacuum source of exhausting air from within the bell jar 11 and thesputtering device 13. A third conduit 21 has one end connected to thevalve and the other end connected to a source of inert gas such as argonor the like so that the gas pressure can be adjusted to the desiredmagnitude. Reactive gases such as oxygen and nitrogen can also be usedwhen metal and dielectric films such as tantalum nitride or aluminumoxide are to be formed. To remove the bell jar II when the platingprocess has been completed, air can be admitted by disconnecting thevacuum source and opening conduit 20 to the atmosphere.

In the instant embodiment of the invention the circular plate 14 has aplurality of openings 22 spaced uniformly from the center of the plateand the work pieces or substrates on which thin films are to bedeposited overlie these openings. During the operation one of the pieces23 is aligned with the sputtering device 13 and is maintained in thatposition until the desired thickness of film is deposited on theunderside thereof. Then without interrupting the operation of the sputtering device 13, the plate 14 is rotated to bring the nest successivework piece into alignment with the sputtering device, and it remains inthat position until the desired film is deposited thereon. The operationis then continued in this manner until all of the work pieces have beencoated. If desired, the plate 14 can be continuously rotated so thateach workpiece or substrate will receive some sputtered material duringeach revolution. Operation of the sputtering device 13 is thenterminated and air is admitted into the bell jar 11 by the valve l9which permits the bell jar to be raised for removal of the coatedworkpieces 23 and placement of the next set of work pieces to be coated.The glow discharge for operating the sputtering device 13 is obtained byapplying substantially zero voltage through lead 24 to the housing orouter casing thereof and a high negative voltage to leads 25 and 26which connect with the cathodes as will be described. A fourth lead 27may be connected with the plate 14 to apply an additional bias voltageto the plate and thus to the workpieces when the latter are of aconductive material.

The sputtering device 13 is shown in detail in FIG. 2 and correspondingelements of FIGS. 1 and 2 have been denoted by like numerak. In theinstant embodiment of the invention. the anode 28 u an essentiallycylindrical tube and has an annular flange 29 which is secured to theunderside of the base 10 by screws or other fastening means 30. Theanode 28 is aligned with an opening 3| in the baseplate l and the flange29 includes an annular seal 32 to insure an airtight attachment of theanode to the baseplate.

A first cathode 33 preferably of a hollow cylindrical configurationextends downwardly through the baseplate and into a portion of the anode28. The top edge of the cathode 33 includes an annular flange 34 havinga recess 35 in the underside thereof for receiving a ring 36 ofinsulating material. The ring 36 may be cemented in the recess 35 and tothe top surface of the base plate to maintain the cathode in concentricrelationship with the anode. With this arrangement, the cathode 33 isinsulated from the anode to permit the application of a high negativevoltage thereto by the lead 25. While it is desirable to have theconfiguration of the cathode 33 conform with the internal configurationof the anode 28, the spacing between the anode and the cathode should beas small as possible in order to prevent a glow discharge from occuringtherebetween. Furthermore, the cathode 33 though illustrated as being oftubular configuration may of course take other suitable forms. It isgenerally desirable however that the cathode have a substantiallyuniform cross-sectional configuration in order to produce more unifonnfilms, but such a configuration may be modified depending on theparticular film requirements. In any event, ion scrubbing can beachieved which enables the attainment of improved adherence of the filmto the substrate and film contamination is materially reduced.

The bottom of the anode 28 is closed by an annular member 37 which ishermetically sealed in position on the anode by an annular weld 38 orother suitable sealing means. The member 37 carries a second cylindricalcathode 39 which is centrally disposed within the anode 28. Thesupporting means for the cathode 39 consists of a metallic sleeve 40which extends through the member 37 and has an annular flange 4] whichengages the top side of the member 37 and is sealed thereto by a gasket42. The lower end of the metallic sleeve 40 has threads 43 for engaginga nut 44 to firmly hold the sleeve 40 in position within the opening 37of the member 37. An insulating sleeve 45 extends through centralopening in the metallic sleeve 40 and a rod 46 of conductive materialextends through the sleeve 45. A spacer 47 of insulating materialsurrounds the upper portion of the insulating sleeve 45 and the cathode39 threadably engages the upper end of the rod 46. The insulating sleeve45 is hermetically sealed to the rod 46 and to the metallic sleeve 40and the lower end of the rod 46 terminates in a contact 48 to which thelead 26 is attached. An annular magnet 49 preferably of permanentlymagnetized material surrounds the anode 28 and the upper end of themagnet preferably extends beyond the lower edge of the upper cathode 33.

With the invention as described above, the anode 28 is connected toground or substantially zero potential by the lead 24 while a voltage ofthe order of 1,000 volts negative is applied to both the leads and 26.Under these conditions the glow discharge can be produced with aninternal pressure of the order of 2X l 0" torr. The magnet 49 produces amagnetic field in the direction of the arrow A at a point centrally ofthe magnet and the cathode 33 is either formed of or carries one of ormore materials to be sputtered. Under these conditions atoms will beliberated from the cathode and more upwardly striking the underside ofthe workpiece 23 and forming a film thereon. In actual practice it hasbeen found that when the cathode 33 is about 2 inches in diameter, it ispreferably to maintain a distance between the underside of the workpiece23 and the lower edge of the cathode 33 of about 6 centimeters. If thisdistance is exceeded, it has been found that the coating rate may bereduced and the film deposited tends to be nonuniform. Furthermore. itis also preferable that the lower edge of the cathode extends below theplane of the upper edge of the permanent magnet 49 a dhtance ofapproximately onequarter of an inch for maximum sputtering efficiency.

in the operation of the device in accordance with the invention. thesubstrate or workpiece whether of a conductive or nonconductive materialattains almost immediately a bias voltage of about 50 volts negativewhen floating electrically. This self-biasing feature is mostadvantageous since the surface of the workpiece is automatically"scrubbed" by ions attracted by the surface, and this increases theadherence of the film to the workpiece. Ion-scrubbing effects removal ofmany contaminants such as water vapor and hydrocarbons which not onlyinterfere with adhesion but also contaminate the film. In prior knowndevices self-biasing voltages of the order of 6 to 8 volts are generallyattained but such voltages are below the threshold for ionbombardmentcleaning and thus have no effect. Moreover, the use of probes forbiasing is not helpful since a conductive base film of at least 50angstroms in thickness is required for alfixing the probe and there isno affect on either the base film or its adhesion to the workpiece. Ifdesired, a bias can be applied to the workpiece 23 by means of lead 27which of course would fix the bias to any desired value. it is of courseevident that the anode of the sputtering device is formed of anonmagnetic material so that the desired magnetic filed will be producedwithin the device.

The form of the invention described in connection with FIG. 2 isparticularly useful when a DC voltage is applied between the anode andthe cathodes and the reentrant cathode 33 extends below the top surfaceof the magnet 49. In this way a high-intensity glow discharge isobtained with a high degree of stability notwithstanding the relativelylow gas pressure within the device. it is believed that thehigh-intensity glow discharge results from the fact that the specificrelationship of the magnetic field to the cathodes deflects electronsfrom the paths which they would normally follow in the absence of such afield with the result that the lengths of such paths are increased. Thisaction increases the number of ionizing collisions between the electronsand the gas molecules and such collisions are necessary in order toobtain a high deposition rate of atoms from the cathode 33 onto the workpiece 23.

A modified embodiment of the invention is illustrated in FIG. 3 anddiffers from the structure shown in FIG. 2 in that the cathode 39 isomitted. Since both forms of the invention are identical with theexception of the cathode 39 corresponding elements are denoted by likenumerals. With the elimination of the cathode 39, the bottom of theanode 28 is merely closed by a plate 28' hermetically sealed thereto.This form of the invention operates in the same manner as the form ofthe invention described in connection with FIG. 2 and produces anautomatic bias on the substrate being plated.

With both forms of the invention described above. operation can beeffected with exceedingly low gas pressures as low as 2X10" torr., whichresults not only in purer films but also in increased adherence of thefilm to the substrate or work piece. Furthermore, since the workpieceneed not be secured to the cathode or anode, the sputtering apparatus isparticularly adaptable for use in continuous production processes asthere are well-known means for moving the substrates in position forplating and removing finished workpieces without interruption ofoperation. While the forms of the invention have been illustrated withthe axis of the anode in a vertical position, it is of course possibleto operate the sputtering device in any desired position.

While only certain embodiments of the invention have been illustratedand described, it is apparent that alterations, modifications andchanges may be made without departing from the true scope and spiritthereof as defined by the appended claims.

lclaim l. Sputtering apparatus for coating a workpiece comprising ananode shell of conductive material having an opening on one end and aconductive closure hermetically sealing the other end, an open-endedtubular cathode at said one end of said anode shell and having at leasta portion disposed within an in close proximity to said anode shell toprovide uninterrupted access into said anode shell, means for supportingwork to be coated at said one end of said anode shell to intercept atomsemerging from the cathode, means hermetically enclosing said one end ofsaid anode shell, said cathode and said work-supporting means and meansproducing magnetic and electric fields in said anode shell with thedirection of said magnetic field being disposed centrally of said anodeshell and substantially axially aligned therewith. said magnetic fieldhaving a nonlinear portion intercepted by said tubular cathode.

2. Sputtering apparatus according to claim I wherein said magnetic fieldgenerating means surrounds said anode shell.

3. Sputtering apparatus according to claim I wherein said cathodeextends from a point spaced outwardly from the other end of said anodeshell into said anode shell and intercepts said nonlinear portion ofsaid magnetic field.

4. Sputtering apparatus according to claim I wherein said magneticfield-generating means comprises a magnet surrounding said shell andwherein said cathode extends inwardly from the other end of said shellto a point beyond the plane defined by the adjoining edge of saidmagnet.

5. Sputtering apparatus according to claim 4 wherein said cathode, hasan average internal diameter of about 2 inches and extends into saidanode a distance at least one fourth inch beyond the plane defined bysaid adjoining edge of said magnet.

6 Sputtering apparatus according to claim 1 including a second cathodewithin and insulated from said anode shell, said second cathode beingpositioned in spaced relationship to the first and cathode andelectrically interconnected therewith.

7. Sputtering apparatus comprising an open-ended tubular anode ofnonmagnetic conductive material, nonmagnetic conductive means closingone end of said anode and electrically connected to said anode, magneticfield means producing magnetic flux within and in a direction generallyin line with the central portion of the axis of the anode and havingnonlinear end portions an open-ended tubular cathode projecting into theother end of said anode and intercepting at least a part of a nonlinearportion of said magnetic field, a work support facing the opening insaid tubular cathode, means enclosing and sealing the other end of saidanode, said cathode and work support whereby said anode can be at leastpartially evacuated and means for applying a voltage between said anodeand cathode to produce a glow discharge causing gas ions to strike saidcathode and liberate atoms from said cathode for deposition on said worksurface.

8. Sputtering apparatus according to claim 7 wherein saidmagnetic-field-producing means includes a permanent magnet surroundingsaid tubular anode and said tubular cathode extends into said anode to apoint beyond the adjoining end of said magnet.

9. Sputtering apparatus according to claim 8 wherein said cathode andmagnet overlap at least one fourth.

l0. Sputtering apparatus according to claim 7 including a second cathodedisposed within and insulated from said anode.

ll. Sputtering apparatus comprising an anode shell of conductivematerial and having an opening on one end and a conductive closurehermetically sealing the other end, an openended tubular cathodeadjoining said open end and at least partially disposed within saidanode shell, means supporting a substrate to be plated in proximity tosaid cathode, means hermetically enclosing said one end of said anodeshell, cathode and work-supporting means to permit evacuation of saidanode shell and produce a gaseous atmosphere therein, and meansproducing electric and magnetic fields within said anode and cathodeshell with at least a portion of the magnetic field bein nonlinear andintercepted by said cathode, said fields pr ucing a glow dischargetherein and causlng atoms released from said cathode to be deposited onsaid substrate and form a film thereon, said electric and magneticfields producing a relatively high negative bias on said substrate toeffect cleaning of said substrate by ion bombardment and minimizecontamination of the film deposited thereon.

l2. Sputtering apparatus according to claim l1 including a secondcathode disposed within said anode and in spaced relationship to thefirst said cathode.

l3. Sputtering apparatus for coating a workpiece comprising a singleopen ended hollow shell, magnetic means surrounding said shell toproduce a magnetic field within said shell having a substantially linearcentral portion and nonlinear end portions, a cathode having an openingtherein adjoining the open end of said shell, the surface of saidopening carrying material to be sputtered, said cathode openingintercepting at least a portion of the nonlinear magnetic field, meansincluding said cathode and an anode for producing an electric fieldwithin said shell and work-supporting means spaced from said cathodeopening and on the side of said cathode opposite said shell.

i i U i Patent No.

3,616,450 Dated October 26, 1971 Peter J. Clarke Inventor(s) It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

On the cover sheet [72] Peter J. Clarke read and "Peter J. Clark",should read Claim 1, line 6, "an" should Signed and sealed this 8th dayof May 1973.

(SEAL) Attest:

EDWARD I LFLETCHEILJR.

Commissioner of Patents USCOMM-DC 60376-P69 u 5 GOVERNMENT Pmmmc orncz:I959 o-3se-3a4,

2. Sputtering apparatus according to claim 1 wherein said magneticfield- generating means surrounds said anode shell.
 3. Sputteringapparatus according to claim 1 wherein said cathode extends from a pointspaced outwardly from the other end of said anode shell into said anodeshell and intercepts said nonlinear portion of said magnetic field. 4.Sputtering apparatus according to claim 1 wherein said magneticfield-generating means comprises a magnet surrounding said shell andwherein said cathode extends inwardly from the other end of said shellto a point beyond the plane defined by the adjoining edge of saidmagnet.
 5. Sputtering apparatus according to claim 4 wherein saidcathode, has an average internal diameter of about 2 inches and extendsinto said anode a distance at lEast one fourth inch beyond the planedefined by said adjoining edge of said magnet.
 6. Sputtering apparatusaccording to claim 1 including a second cathode within and insulatedfrom said anode shell, said second cathode being positioned in spacedrelationship to the first said cathode and electrically interconnectedtherewith.
 7. Sputtering apparatus comprising an open-ended tubularanode of nonmagnetic conductive material, nonmagnetic conductive meansclosing one end of said anode and electrically connected to said anode,magnetic field means producing magnetic flux within and in a directiongenerally in line with the central portion of the axis of the anode andhaving nonlinear end portions, an open-ended tubular cathode projectinginto the other end of said anode and intercepting at least a part of anonlinear portion of said magnetic field, a work support facing theopening in said tubular cathode, means enclosing and sealing the otherend of said anode, said cathode and work support whereby said anode canbe at least partially evacuated and means for applying a voltage betweensaid anode and cathode to produce a glow discharge causing gas ions tostrike said cathode and liberate atoms from said cathode for depositionon said work surface.
 8. Sputtering apparatus according to claim 7wherein said magnetic-field-producing means includes a permanent magnetsurrounding said tubular anode and said tubular cathode extends intosaid anode to a point beyond the adjoining end of said magnet. 9.Sputtering apparatus according to claim 8 wherein said cathode andmagnet overlap at least one fourth inch.
 10. Sputtering apparatusaccording to claim 7 including a second cathode disposed within andinsulated from said anode.
 11. Sputtering apparatus comprising an anodeshell of conductive material and having an opening on one end and aconductive closure hermetically sealing the other end, an open-endedtubular cathode adjoining said open end and at least partially disposedwithin said anode shell, means supporting a substrate to be plated inproximity to said cathode, means hermetically enclosing said one end ofsaid anode shell, cathode and work-supporting means to permit evacuationof said anode shell and produce a gaseous atmosphere therein, and meansproducing electric and magnetic fields within said anode and cathodeshell with at least a portion of the magnetic field being nonlinear andintercepted by said cathode, said fields producing a glow dischargetherein and causing atoms released from said cathode to be deposited onsaid substrate and form a film thereon, said electric and magneticfields producing a relatively high negative bias on said substrate toeffect cleaning of said substrate by ion bombardment and minimizecontamination of the film deposited thereon.
 12. Sputtering apparatusaccording to claim 11 including a second cathode disposed within saidanode and in spaced relationship to the first said cathode. 13.Sputtering apparatus for coating a workpiece comprising a single openended hollow shell, magnetic means surrounding said shell to produce amagnetic field within said shell having a substantially linear centralportion and nonlinear end portions, a cathode having an opening thereinadjoining the open end of said shell, the surface of said openingcarrying material to be sputtered, said cathode opening intercepting atleast a portion of the nonlinear magnetic field, means including saidcathode and an anode for producing an electric field within said shelland work-supporting means spaced from said cathode opening and on theside of said cathode opposite said shell.